Thick film dielectric structures as exemplified by U.S. Pat. No. 5,432,015 (the entirety of which is incorporated herein by reference) are typically fabricated on ceramic substrates and provide superior resistance to dielectric breakdown, as well as a reduced operating voltage compared to thin film electroluminescent (TFEL) displays fabricated on glass substrates. When deposited on a ceramic substrate, the thick film dielectric structure withstands higher processing temperatures than TFEL devices on glass substrates. The increased tolerance to higher temperatures facilitates annealing of the phosphor films at higher temperatures to improve luminosity. However, even with the enhanced luminosity that is obtained, it is desirable to further increase the luminous efficiency of the devices to enable an improvement in overall energy efficiency and reduction in power consumption.
The Applicant has developed various methods for the deposition of phosphors used in a thick film dielectric electroluminescent device. For example, PCT CA01/01823 (the disclosure of which is incorporated herein in its entirety) discloses a method, preferably electron beam vaporization, for the deposition of a ternary, quaternary or similar phosphor composition, in which components of the composition are located on different sources. In particular, the compositions are thioaluminates, thiogallates or thioindates of Group IIA and Group IIB elements, and the sulfides that form such compounds are located on the different sources. PCT CA01/01234 (the disclosure of which is incorporated herein in its entirety) discloses a dual source phosphor deposition method using dual source electron beam deposition. The various compounds of the first and second sources are in the ratios required to provide the required composition of the phosphor. The deposited phosphors are preferably blue emitting europium activated barium thioaluminate. PCT CA02/00688 (the disclosure of which is incorporated herein in its entirety) discloses a single-source sputtering method for depositing controlled composition multi-element phosphor films. The method utilizes a source material in the form of a single dense target that has a composition different from the desired film composition of the phosphor. The concentrations of light chemical elements relative to heavier chemical elements in the target composition of the process is higher than desired in the deposited films.
The aforementioned patent applications disclose desirable phosphors and methods to deposit the phosphors for use in thick film dielectric electroluminescent displays. However, it is always desirable to provide new methods to further improve luminance and luminous efficiency of the phosphor compositions.